The invention generally relates to equipment and processes for in-line manufacture of absorbent products. The equipment and the process utilize synthetic resins, such as thermoplastics, for the in-line manufacture of a multi-layer absorbent product. The invention also relates to a composite absorbent product comprising at least an impervious nonwoven bottom sheet, an absorbent nonwoven core, and a nonwoven top sheet.
The equipment used for in-line manufacture of absorbent products, such as diapers, sanitary napkins, adult incontinent pads and the like, is generally referred to as converter equipment and the process is generally referred to as converting. The converter equipment processes separate rolls of stock material into the composite absorbent product. The converter equipment generally comprises stations for manufacturing the composite absorbent product as follows:
(a) An absorbent core forming station comprising a hammermill is fed by pulp roll stock, such as cellulosic material with or without superabsorbent. The hammermill fiberizes the pulp, and a drum form or flat screen then forms the fiberized pulp. Alternatively, the absorbent core material can be supplied in roll form.
(b) A top sheet station supplies a top sheet or coverstock layer comprising a nonwoven, such as spunbond polypropylene. The top sheet is unwound from a roll and applied to the core layer.
(c) A bottom sheet station for supplying a liquid-impervious backsheet, such as polyethylene film, which is applied to the top sheet/core combination.
The absorbent product is a composite comprising a top sheet or cover stock, an intermediate core layer of absorbent material, and a bottom sheet or back sheet of impervious film. Most converter equipment includes devices for adding a variety of options, such as elastic waistbands and legbands, tab applicators, frontal tape applicators, transfer layers, and the like.
A characteristic common to all converter equipment and processes is that they use only roll stock to form the layers of the absorbent product. The roll stocks are separately manufactured into rolls, typically off site, and then transported to the site of use. These rolls are processed by the converter equipment to form multiple layer absorbent products.
Converter equipment typically comprises a large complex laminating machine which requires significant horizontal and vertical plant space. The complex equipment requires constant attention and fine tuning. Also, converter equipment generally produces a one-line output so the unit output is directly proportional to the line speed. Accordingly, the converter equipment must operate at extremely high speed, such as at line speeds of 700 to 1200 ft./min., to be economical.
As the converter equipment handles only preformed roll stock, it has a serious operational disadvantage. That is, once the multiple rolls are installed, the composition, properties or dimensions of the roll stocks cannot be changed. In order to produce two different types of absorbent products, or absorbent products with different properties, the converter must be shut down and a new roll or rolls substituted for the existing roll or rolls. For these reasons, it would be desirable to eliminate one or, preferably, more of the conventional roll stocks and form different layers of an absorbent composite product in-line.
The method and apparatus of the present invention most preferably involve fiberizing or melt spinning a synthetic resin, such as thermoplastic, at three separate stations. These three stations comprise a top sheet forming station, a core layer forming station, and a bottom sheet forming station.
The top sheet forming station includes at least one fiberizing die, such as a spunbond die, to form a nonwoven top sheet which is delivered in-line to a combining station. The bottom sheet forming station includes at least one spunbond die and, preferably, one or more additional meltblowing dies to form a water-impervious composite bottom sheet. The bottom sheet is preferably conveyed directly (in-line) to the core layer forming station where one or more meltblowing dies deposit a meltblown layer or a plurality of meltblown sublayers onto the bottom sheet to form a bottom sheet/core layer composite. The bottom sheet/core layer composite is conveyed in-line to the combining station where it is laminated with the top sheet to form an absorbent composite in accordance with the invention. In particular, the absorbent composite of this invention preferably comprises:
(a) an inner top sheet of strong, fluid-permeable nonwoven;
(b) a middle absorbent core layer of a nonwoven composed of hydrophilic microsized fibers, with preferably a sublayer of a coarser nonwoven in contact with the top sheet to aid in distributing liquid permeating the top sheet; and
(c) a substantially fluid-impermeable back sheet of a strong nonwoven for containing the core layer and retaining fluid collected or absorbed therein.
Variations in the invention include using fiberizing dies at two stations, such as the top sheet and core layer forming stations, with roll stock used at the third station. Other variations of fiberizing dies and roll stock may be used as well. Also, the three layers may be affixed to one another, whether using fiberizing dies or roll stock, in various orders not withstanding that a preferred order of manufacture is specifically described herein.
The absorbent composite may be made an overall width transverse to the machine direction equal to multiple widths of each individual absorbent product. In such an embodiment, the composite width is slit longitudinally along the machine direction to form a plurality of slits, each slit being equal to the width of one absorbent product. The slits are then cut at longitudinal intervals to form individual absorbent products.
As described herein, the present invention contemplates several embodiments. Advantages and distinguishing features of some or all embodiments may be summarized as follows:
(1) The absorbent composite comprises three or more layers or sheets of microsized fibers.
(2) Fiberizing or melt spinning of each component sheet or layer of the composite avoids the need for a converter. Thermoplastic resin is processed on site to form the compound sheets or layers and conveyed in-line to the combining station.
(3) The in-line manufacture of the component sheets or layers permits the rapid and easy change of materials (e.g., polymer grade), properties of the sheets or layers, and operating conditions.
(4) The manufacture of the large widths equal to several widths of individual absorbent products permits the line to operate at only a fraction of the speed of converters in achieving the same unit output.
Additional objectives, advantages and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings.